The present invention relates to nuclear magnetic resonance (NMR) imaging and spectroscopy and, more particularly, to novel methods for providing NMR images containing spatially-localized information about chemical reaction, or metabolic turnover rates between selected chemical species.
Hitherto, positron emission tomography (PET) was virtually unique in providing information about metabolic turnover, or chemical-species reaction rates, useable in medical diagnosis of human beings. However, because the PET image intensity is derived directly from substances which must be introduced into the human body via the bloodstream, the metabolic information for a region of tissue of interest is obscured by the amount of blood flow, the vascularization and even the number of tissue cells present in that tissue region. It is desirable to provide a non-invasive procedure. Further, because PET requires the use of a cyclotron, the cost of each PET metabolic imaging procedure is much more expensive than the cost of a typical NMR imaging procedure; consequently, PET useage is presently reserved for research, rather than everyday routine clinical, diagnostic use. It is highly desirable to provide a procedure in which the chemical reaction rate of a selected chemical species can be measured in each of a plurality of spatially-localized volume elements (voxels), and in which the resulting chemical reaction rate information can be made available for display and analysis. It is known, as described in "Nuclear Magnetic Resonance and its Applications to Living Systems", David G. Gadian, Clarendon Press, Oxford (1982), that saturation-transfer and inversion-transfer NMR spectroscopy techniques can be utilized for measuring whole-sample chemical reaction rates or metabolic turnover rates. However, there has hitherto been no method for obtaining a suitable NMR signal which is substantially proportional to the chemical reaction rate in a localized volume of a heterogeneous sample, to allow noninvasive measurement of metabolic turnover in normal and diseased tissue in voxels of living human beings, while directly observing naturally-abundant metabolites involved in human biochemical reactions, without obscuration of the voxel reaction rate information by flow, vascularization or cell density.